Well, I think it's a bug :) Setting a linecap style makes casing-color
get ignored.
Here's the code I was using:
way[highway=service][divider=median]
{
z-index:1;
color:white;
width:7;
casing-color:blue;
casing-width:36;
linecap:round;
}
(casing renders as black. remove the linecap line, it renders as blue.
Lat: -37.82199
Lon: 144.919573
Steve